Thesis (M.S.)--Ohio University, November, 1994. / Title from PDF t.p.

Thesis (M.S.)--Ohio University, June, 2002.

This master's thesis is concerned with the basis of ultra-acoustics and it explains the application of Doppler effect in medicine as a diagnostic method used for measuring blood flow velocity in blood vessels. The thesis also presents Doppler systems used for diagnostic purposes. It describes the principles of these systems, shows accompanying flowcharts and explains the function of these systems. There is also included the system design of the whole ultrasonic blood flow velocity meter. The system has been designed for the specified parameters with continuous 4 MHz operating frequency, generated intensity of ultrasound 100 mW/cm^2 and diameter D-shaped transmitting transducer 8 mm. In the design of personal solution there are described all the function blocks of the ultrasonic meter. There is also described the choice of appropriate components and designed all the required supply voltages. All the function blocks of the system are experimentally verified. The system has been designed with acoustic intercept and the resultant velocity curves are displayed on software oscilloscope on PC.

Doppler effects on vehicular communication have been theoretically modeled by many researchers. However, very limited experimental studies have been conducted to investigate the impact of Doppler shift on the vehicle-to-vehicle (V2V) communication range and reliability with high speed mobility. The current work-in-progress research aims to quantify the impact of Doppler effects on V2V communication reliability, range, and reachability using singlehop Dedicated Short Range communications (DSRC) between two opposite traffic. We conducted our experiments by mounting the after-market DSRC on-board units on the dashboard of two vehicles that cross each other from opposite directions with constant relative speeds on a real interstate freeway. Our preliminary results indicate that the communication time and range drop to approximately 70% and 40% after the two vehicles cross and start moving away from each other with the average relative speeds of 110 and 140 mph, respectively. Similarly, the packet delivery ratio is also drastically reduced after the vehicles start moving away from each other. Apparently, these results indicate that there might be a strong effect of Doppler phenomena on the transmission range, packet delivery rate and the duration of the communication.

No description available.

The effect of selected anthropometric indices on the reproducibility of continuous wave (CW) Doppler echocardiographic recordings in exercise were studied in 42 healthy males between 18 and 43 years of age. Each subject was measured and rank ordered in reference to four anthropometric Indices: sum of 3 skinfolds (SK); chest girth-waist girth ratio (CW); biacromial width-chest depth ratio (WD); and peak exercise ventilationâ forced vital capacity ratio (VV). Each subject then performed two maximal bicycle exercise tolerance tests on nonconsecutive days wherein the CW Doppler variables of peak acceleration (pKA), peak velocity (pKV) and stroke velocity integral (SVI) were measured along with heart rate (HR), blood pressure (BP) and respiratory gas analysis data including oxygen consumption (V0₂). Statistical analyses were then conducted to determine if subject groups with high vs. low values on any anthropometric index differentiated with regard to testâ retest reliability between bicycle exercise test trials. Statistical differences were noted between ( the high and a low groups for each index at the .05 alpha level. Pearson's Product Moment correlational analyses revealed that across all subjects the highest test-retest reliability occurred during the moderate intensity of exercise. The average test-retest correlation coefficients for the high and low groups within each index are as follows: SK_H, = .52, SK_L = 62, CW_H = .64, CW_L = .60, WD_H. = 62,WD_L = 58, VV_h. = 61, VV_L = .67. Inspection of test-retest correlations between the high vs. low groups for the anthropometric indicies revealed a trend in the skinfold index. For each dependent measure at all levels of exercise intensity, the low group exhibited higher correlation coefficients than the high group except for pKA at the peak level of exercise. The other three indicies exhibited no such trends. lt was concluded that since The other three indicies exhibited no such trends. lt was concluded that since the overall correlation coefficients (average = .65) were within the ranges of those computed for HR. BP and VO₂; (average = .50) the test-retest reliability with the CW Doppler was acceptable; but only during moderate levels of exercise. It was also determined from the correlation coefficients generated by the skinfold index data that measures obtained on lean individuals may be moree reproducible than measures obtained from obese individuals (See Table 2). / Master of Science

Pulsed ultrasound Doppler velocimetry proved to be capable of measuring velocities accurately (relative error less than 0.5 percent). In this research, the limitations of the method are investigated when measuring: in channels with a small thickness compared to the transducer diameter, at low velocities and in the presence of a flow reversal area. A review of the fundamentals of pulsed ultrasound Doppler velocimetry reveals that the accuracy of the measured velocity field mainly depends on the shape of the acoustic beam through the flow field and the intensity of the echo from the incident particles where the velocity is being measured. The ultrasonic transducer turned out to be most critical component of the system. Fundamental limitations of the method are identified. With ultrasonic beam measurements, the beam shape and echo intensity is further investigated. In general, the shape of the ultrasonic beam varies depending on the frequency and diameter of the emitter as well as the characteristics of the acoustic interface that the beam encounters. Moreover, the most promising transducer to measure velocity profiles in small channels is identified. Since the application of pulsed ultrasound Doppler velocimetry often involves the propagation of the ultrasonic burst through Plexiglas, the effect of Plexiglas walls on the measured velocity profile is analyzed and quantified in detail. The transducers ringing effect and the saturation region caused by highly absorbing acoustic interfaces are identified as limitations of the method. By comparing measurement results in the small rectangular channel to numerically calculated results, further limitations of the method are identified. It was not possible to determine velocities correctly throughout the whole channel at low flow rates, in small geometries and in the flow separation region. A discrepancy between the maximum measured velocity, velocity profile perturbations and incorrect velocity determination at the far channel wall were main shortcomings. Measurement results are improved by changes in the Doppler angle, the flow rate and the particle concentration. Suggestions to enhance the measurement system, especially its spatial resolution, and to further investigate acoustic wave interactions are made.

This study focuses on challenges and prospects of the teaching of the Doppler Effect to grade 12 learners. The challenges of teaching the Doppler Effect were established and these findings influenced the development of activities. These activities were tested, refined and re-tested in an iterative cycle and finally provided prospects on teaching the Doppler Effect. Educational Design Research (EDR) was used to bridge theory and practice in education. This study was done in the Vhembe district in the Limpopo province. In the first cycle, questionnaires and interviews with 32 teachers and a subject advisor were used to establish the baseline with regards to the challenges of teaching the Doppler Effect. After the analysis of the data which forms the first cycle of EDR, the content and methodological problems faced by teachers when teaching the Doppler Effect were revealed. In the second cycle of the EDR, learning activities were developed that was informed by the analysis and tried out in 2 schools by learners and their teachers. Completed activity sheets were marked and the results were used to determine if there were a correlation between the activity sheets and the written test. Problems were documented and changes to the activities were again made and tried out in 10 schools by 216 learners with the help of 10 teachers. The data collected from the learners` work sheets were analysed. Pearson`s product moment correlation has shown that there is a statistically significant relationship (r = 0.65; p < 0.01) that exists between these design-research activities and solving of problems on the Doppler Effect. An instructional manual was developed comprising of the final activities. This was distributed amongst the district officials and teachers to assist them in the teaching of the Doppler Effect in the Vhembe district. / Physics / M.Sc.(Mathematics, Science and Technology Education)

This study focuses on challenges and prospects of the teaching of the Doppler Effect to grade 12 learners. The challenges of teaching the Doppler Effect were established and these findings influenced the development of activities. These activities were tested, refined and re-tested in an iterative cycle and finally provided prospects on teaching the Doppler Effect. Educational Design Research (EDR) was used to bridge theory and practice in education. This study was done in the Vhembe district in the Limpopo province. In the first cycle, questionnaires and interviews with 32 teachers and a subject advisor were used to establish the baseline with regards to the challenges of teaching the Doppler Effect. After the analysis of the data which forms the first cycle of EDR, the content and methodological problems faced by teachers when teaching the Doppler Effect were revealed. In the second cycle of the EDR, learning activities were developed that was informed by the analysis and tried out in 2 schools by learners and their teachers. Completed activity sheets were marked and the results were used to determine if there were a correlation between the activity sheets and the written test. Problems were documented and changes to the activities were again made and tried out in 10 schools by 216 learners with the help of 10 teachers. The data collected from the learners` work sheets were analysed. Pearson`s product moment correlation has shown that there is a statistically significant relationship (r = 0.65; p < 0.01) that exists between these design-research activities and solving of problems on the Doppler Effect. An instructional manual was developed comprising of the final activities. This was distributed amongst the district officials and teachers to assist them in the teaching of the Doppler Effect in the Vhembe district. / Physics / M.Sc. (Mathematics, Science and Technology Education)

Approved for public release; distribution is unlimited / The IEEE 802.11a standard uses a coded orthogonal frequency division multi-plexing (COFDM) scheme in the 5-GHz band to support data rates up to 54 Mbps. The COFDM was chosen because of its robustness to multipath fading affects. In the stan-dard, convolutional codes are used for error correction. This thesis examines the perform-ance of the COFDM system with variable rate Reed-Muller (RM) error correction codes with a goal to reduce the peak-to-average power ratio (PAPR). Contrary to the expecta-tions, RM codes did not provide expected improvement in PAPR reduction. Peak clip-ping and Hanning windowing techniques were investigated in order to reduce the PAPR. The results indicate that a tradeoff exists between the PAPR and the bit-error rate (BER) performance. Although peak clipping yielded considerable reduction in PAPR, it required high signal-to-noise ratios. On the other hand, Hanning windowing provided only a small reduction in PAPR with reasonable BER performance. / Lieutenant Junior Grade, Turkish Navy